U.S. patent application number 10/865322 was filed with the patent office on 2005-12-15 for method and apparatus for measuring temperature and emissivity.
Invention is credited to Pint, Charles Steven.
Application Number | 20050276308 10/865322 |
Document ID | / |
Family ID | 34971456 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050276308 |
Kind Code |
A1 |
Pint, Charles Steven |
December 15, 2005 |
Method and apparatus for measuring temperature and emissivity
Abstract
Apparatuses for measuring temperature and emissivity, and
methods of measuring temperature and emissivity are disclosed
wherein the apparatus may include a processor adapted to execute an
algorithm to adjust emissivity values until a desired temperature
calculation is achieved. Accordingly, tedious manual adjustment
steps by an operator are unnecessary.
Inventors: |
Pint, Charles Steven;
(Evanston, IL) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
233 S. WACKER DRIVE, SUITE 6300
SEARS TOWER
CHICAGO
IL
60606
US
|
Family ID: |
34971456 |
Appl. No.: |
10/865322 |
Filed: |
June 10, 2004 |
Current U.S.
Class: |
374/121 ;
374/128 |
Current CPC
Class: |
G01J 5/0003
20130101 |
Class at
Publication: |
374/121 ;
374/128 |
International
Class: |
G01J 005/00 |
Claims
1. A method of measuring emissivity of a target, comprising:
inputting a first temperature; receiving data from a detector, the
data indicative of the target temperature; setting an initial
emissivity value; setting an emissivity step size; setting a
threshold; calculating a second temperature based on the data and
the emissivity value; calculating a difference between the second
temperature and the first temperature; comparing the difference to
the threshold; adjusting the emissivity value if the second
temperature surpasses the threshold, the emissivity value adjusted
by the emissivity step size, the second temperature recalculated
using the adjusted emissivity value; and saving the emissivity
value if the second temperature is within the threshold.
2. The method of claim 1, wherein the adjusting of the emissivity
value and the temperature recalculation repeat until the second
temperature is within the threshold.
3. The method of claim 2, wherein the repeating stops if the
emissivity value exceeds a pre-determined boundary.
4. The method of claim 1, further including dividing the step size
in half.
5. The method of claim 1, further including receiving a plurality
of data from the detector, the plurality of data averaged for a
time period.
6. The method of claim 1, further including receiving a plurality
of data from the detector, the plurality of data averaged for a
pre-determined number of data points.
7. The method of claim 1, wherein the initial emissivity value is
0.5.
8. The method of claim 1, wherein the emissivity value is increased
by the step size if the second temperature is higher than the first
temperature.
9. The method of claim 8, wherein the emissivity value is checked
against an upper threshold.
10. The method of claim 9, wherein the upper threshold is 1.0.
11. The method of claim 1, wherein the emissivity value is
decreased by the step size if the second temperature is lower than
the first temperature.
12. The method of claim 11, wherein the emissivity value is checked
against a lower threshold.
13. The method of claim 12, wherein the lower threshold is
0.01.
14. The method of claim 1, wherein the emissivity value is adjusted
using an algorithm.
15. The method of claim 14, wherein the algorithm is a binary
search algorithm.
16. The method of claim 1, wherein the detector is an infrared
detector.
17. The method of claim 16, wherein the detector measures a single
wavelength.
18. The method of claim 16, wherein the detector measures multiple
wavelengths.
19. An apparatus for measuring temperature, comprising: a
controller comprising a processor, an input and a memory, the input
and the memory operatively coupled to the processor, the input
receiving a first temperature value and saving it to the memory;
and a temperature sensing device, the temperature sensing device
providing data to the processor, the processor selecting an
emissivity value, the processor further calculating a second
temperature using the data and the emissivity value, the processor
calculating a difference between the first temperature value and
the second temperature, the processor comparing the difference
against a threshold, the processor automatically adjusting the
emissivity value if the threshold is exceeded; the processor
automatically saving the emissivity value to the memory if the
threshold is not exceeded.
20. The apparatus of claim 19, wherein the temperature sensing
device is an infrared detector.
21. The apparatus of claim 20, wherein the infrared detector
measures a single wavelength.
22. The apparatus of claim 20, wherein the infrared detector
measures multiple wavelengths.
23. The apparatus of claim 19, wherein the processor repeatedly
calculates the second temperature, calculates the difference
between the first temperature value and the second temperature,
compares the difference against the threshold, and automatically
adjusts the emissivity value until the threshold is not
exceeded.
24. The apparatus of claim 19, wherein the processor stops
adjusting the emissivity value if a predetermined emissivity value
threshold is exceeded.
25. The apparatus of claim 19, further including an algorithm to
automatically adjust the emissivity value.
26. The apparatus of claim 25, wherein the algorithm is a binary
search algorithm.
27. The apparatus of claim 19, wherein the controller is a
programmable logic controller.
28. A method of measuring E-Slope of a target, comprising:
inputting a first temperature; receiving data from a detector, the
data indicative of the target temperature; setting an initial
E-Slope value; setting an E-Slope step size; setting a threshold;
calculating a second temperature based on the data and the E-Slope
value; calculating a difference between the second temperature and
the first temperature; comparing the difference to the threshold;
adjusting the E-Slope value if the second temperature surpasses the
threshold, the E-Slope value adjusted by the E-Slope step size, the
second temperature recalculated using the adjusted E-Slope value;
and saving the E-Slope value if the second temperature is within
the threshold.
29. The method of claim 28, wherein the adjusting of the E-Slope
value and the temperature recalculation repeat until the second
temperature is within the threshold.
30. The method of claim 29, wherein the repeating stops if the
E-Slope value exceeds a pre-determined boundary.
31. The method of claim 28, further including dividing the step
size in half.
32. The method of claim 28, further including receiving a plurality
of data from the detector, the plurality of data averaged for a
time period.
33. The method of claim 28, further including receiving a plurality
of data from the detector, the plurality of data averaged for a
pre-determined number of data points.
34. The method of claim 28, wherein the initial E-Slope value is
1.0.
35. The method of claim 28, wherein the E-Slope value is increased
by the step size if the second temperature is higher than the first
temperature.
36. The method of claim 35, wherein the E-Slope value is checked
against an upper threshold.
37. The method of claim 36, wherein the upper threshold is 1.2.
38. The method of claim 28, wherein the E-Slope value is decreased
by the step size if the second temperature is lower than the first
temperature.
39. The method of claim 38, wherein the E-Slope value is checked
against a lower threshold.
40. The method of claim 39, wherein the lower threshold is
0.80.
41. The method of claim 28, wherein the E-Slope value is adjusted
using an algorithm.
42. The method of claim 41, wherein the algorithm is a binary
search algorithm.
43. The method of claim 28, wherein the detector is an infrared
detector.
44. The method of claim 43, wherein the detector measures multiple
wavelengths.
45. An apparatus for measuring temperature, comprising: a
controller comprising a processor, an input and a memory, the input
and the memory operatively coupled to the processor, the input
receiving a first temperature value and saving it to the memory;
and a temperature sensing device, the temperature sensing device
providing data to the processor, the processor selecting an E-Slope
value, the processor further calculating a second temperature using
the data and the E-Slope value, the processor calculating a
difference between the first temperature value and the second
temperature, the processor comparing the difference against a
threshold, the processor automatically adjusting the E-Slope value
if the threshold is exceeded; the processor automatically saving
the E-Slope value to the memory if the threshold is not
exceeded.
46. The apparatus of claim 45, wherein the temperature sensing
device is an infrared detector.
47. The apparatus of claim 46, wherein the infrared detector
measures multiple wavelengths.
48. The apparatus of claim 45, wherein the processor repeatedly
calculates the second temperature, calculates the difference
between the first temperature value and the second temperature,
compares the difference against the threshold, and automatically
adjusts the E-Slope value until the threshold is not exceeded.
49. The apparatus of claim 45, wherein the processor stops
adjusting the E-Slope value if a pre-determined E-Slope value
threshold is exceeded.
50. The apparatus of claim 45, further including an algorithm to
automatically adjust the E-Slope value.
51. The apparatus of claim 50, wherein the algorithm is a binary
search algorithm.
52. The apparatus of claim 45, wherein the controller is a
programmable logic controller.
Description
FIELD OF THE DISCLOSURE
[0001] The disclosure generally relates to methods of non-contact
temperature measurement and, more particularly, relates to a method
for determining an emissivity value of an object.
BACKGROUND OF THE DISCLOSURE
[0002] Non-contact temperature instruments allow a user to
ascertain the temperature of an object at a distance and are quick
to respond. These operating features are particularly helpful when
measuring the temperature of an object in a harsh or dangerous
environment where physical contact is not an option. Such
instruments generally operate by sensing the energy emitted from
objects at a temperature above absolute zero in which the radiant
infrared energy emitted by the object is proportional to the fourth
power of its temperature.
[0003] Accuracy of the measured temperature is particularly
dependant upon knowing the emissivity of the object. An object may
absorb energy, transmit energy, and reflect energy. The law of
conservation of energy dictates that the sum of coefficients for
absorption, transmission, and reflection add up to 1. However, most
objects are opaque, thus removing the transmission coefficient.
Additionally, the absorptivity is synonymous with emissivity and is
a measure of the ratio of thermal radiation emitted by an object to
that of a blackbody. Generally speaking, emissivity is the ability
of an object to absorb or emit energy. Blackbodies are perfect
emitters and have an emissivity value of 1. An object with, for
example, an emissivity of 0.75 will absorb 75% of the incident
energy and reflect the remaining 25% (assuming no transmission). An
infrared sensor senses energy from all three coefficients
(absorption, transmission, and reflection) and, thus, must be
calibrated to ignore all energy sources except for absorption,
i.e., emissivity.
[0004] Users of such non-contact temperature instruments must
typically input an emissivity value manually before operating the
instrument. The instrument typically has a display area showing
both the emissivity setting, temperature, and various adjustment
buttons/switches. Tables are commonly available which state the
emissivity for various materials at specific temperatures and under
ideal conditions. Unfortunately, conditions may not be ideal due to
the object having surface dust, oil films, and atmospheric
particulate causing erroneous temperature measurements based on an
"ideal" emissivity value.
[0005] Alternately, users may empirically determine an accurate
emissivity value for the instrument by first measuring the surface
temperature of the object with a contact-type temperature probe
(e.g., thermocouple). While simultaneously viewing the temperature
on the display, the user adjusts the emissivity setting until the
temperature reading on the instrument display matches that of the
contact-type temperature probe. At this point, the instrument may
accurately measure the temperature for that specific material in
similar environmental conditions.
[0006] While this process effectively allows the user to determine
and set the emissivity, this process is tedious and requires
numerous key strokes to make the proper adjustment. Furthermore,
market demands require physically smaller instruments that do not
allow the luxury of displays large enough to simultaneously show
temperature, emissivity, and adjustment buttons/switches. The size
limitations allow only a temperature display with some status
indicators.
[0007] It would, therefore, be advantageous to set the emissivity
for a non-contact temperature instrument automatically, which
minimizes or eliminates manual data input by a user.
SUMMARY OF THE DISCLOSURE
[0008] In accordance with one aspect of the disclosure, a method of
measuring emissivity of a target is disclosed which may comprise
inputting a first temperature and receiving data from a detector,
the data indicative of the target temperature. The method may also
comprise setting an initial emissivity value, setting an initial
emissivity step size, setting a threshold, and calculating a second
temperature based on the data and the emissivity value. The method
may calculate a difference between the second temperature and the
first temperature and compare the difference to the threshold.
Additionally, the method may adjust the emissivity value if the
second temperature surpasses the threshold, the emissivity value
adjusted by the emissivity step size, and the second temperature
recalculated using the adjusted emissivity value. Furthermore, the
method may comprise saving the emissivity value if the second
temperature is within the threshold.
[0009] In accordance with another aspect of the disclosure, an
apparatus for measuring temperature is disclosed which may comprise
a controller having a processor, an input and a memory. The input
and the memory may be operatively coupled to the processor, the
input receiving a first temperature value and saving it to the
memory. The apparatus may also comprise a temperature sensing
device, the temperature sensing device providing data to the
processor, the processor selecting an emissivity value, the
processor further calculating a second temperature using the data
and the emissivity value. The apparatus for measuring temperature
may also comprise the processor calculating a difference between
the first temperature value and the second temperature, the
processor comparing the difference against a threshold, the
processor automatically adjusting the emissivity value if the
threshold is exceeded, and the processor automatically saving the
emissivity value to the memory if the threshold is not
exceeded.
[0010] These and other aspects and features of the disclosure will
become more readily apparent upon reading the following detailed
disclosure when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block diagram of one embodiment of an apparatus
for measuring temperature and emissivity in accordance with the
teachings of the disclosure;
[0012] FIG. 2 is a flow chart representative of one embodiment of a
method for measuring temperature and emissivity in accordance with
the teachings of the disclosure.
[0013] While the disclosure is susceptible to various modifications
and alternative constructions, certain illustrative embodiments
thereof are shown in the drawings and will be described below in
detail. It should be understood, however, that there is no
intention to limit the disclosure to the specific embodiments
disclosed, but on the contrary, the intention is to cover all
modifications, alternative constructions, and equivalents falling
within the spirit and scope of the disclosure as defined by the
appended claims.
DETAILED DESCRIPTION
[0014] Referring now to the drawings, and with specific reference
to FIG. 1, an apparatus for measuring temperature constructed in
accordance with the teachings of the disclosure is generally
referred to by reference numeral 100. While the apparatus 100 can
be used to measure the temperature of many objects, examples
include, but are not limited to metal, glass, ceramics, and
plastic.
[0015] FIG. 1 shows the apparatus for measuring temperature 100 in
block diagram format. A controller 105 comprises a processor 110 in
which the processor 110 is operatively coupled to an input 115 and
a memory 120. The processor 110 is further coupled to a temperature
sensing device 125 which may comprise a detector sensitive to
infrared radiation. The detector converts the infrared radiation
energy from an object 130 to an electrical signal where the
magnitude of that signal is used to calculate temperature.
[0016] As stated earlier, however, an accurate temperature
calculation requires an appropriate emissivity value. Calculation
of the appropriate emissivity value requires not only the signal
from the temperature sensing device 125, but also a desired target
temperature set point. The target temperature set point is entered
via the input 115 and saved in the memory 120. Target temperature
set point values may be entered manually by an operator via any
known computer interface such as a keyboard, or optionally, by a
computer, another controller, programmable logic controller (PLC),
PDA, wired, or wireless signal. Further detail regarding
calculation of the appropriate emissivity value will be discussed
herein, however, the memory 120 also stores various algorithms,
such as a binary search algorithm 135, which can be used in that
calculation. Optionally, the apparatus may have an output 140
comprised of a character display (as shown in FIG. 1).
Alternatively, the apparatus 100 may simply produce an output
signal for industry standard devices, including LCD screens,
computers, PLC's, and PDA's.
[0017] FIG. 2 shows a general flowchart of a method for measuring
temperature in accordance with the teachings of the disclosure. The
method may begin at 200 in which step 205 accepts a desired
temperature input of an object. This temperature is typically
obtained in a more traditional contact-type measurement, such as a
bulb thermometer, resistance temperature detector (RTD),
thermocouple (TC), or similar. Assuming that the object maintains
the same temperature throughout this process, this input only needs
to occur once as the temperature input data is saved to the memory
120. The input can come from an operator manually entering the
desired temperature, or alternatively, entered as part of an
automated process.
[0018] Step 210 acquires one or more samples of data from the
temperature sensing device 125. The duration or number of data
samples acquired may be a user-selectable parameter. Step 215
averages the data acquired at step 210 and saves it to memory 120
for later calculation. An emissivity starting point is set at step
220 that may simply be a mid-point of 0.5, or closer to a
"ball-park" set point based on some knowledge of the emissivity of
the object under test. For example, if the user knows the object
130 is an oxidized iron material around 100.degree. C., then an
emissivity of approximately 0.74 might be appropriate. Other
materials would, of course, have other emissivity values generally
ranging from 0.01 to 1.0. Again, the emissivity starting point
parameter, as well as the emissivity step size (step 225), may be
user-selectable. Additionally, emissivity upper and lower
boundaries may also be user-selectable.
[0019] An initial temperature calculation occurs at step 230 using
the emissivity starting point and the data acquired from the
temperature sensing device 125. The processor 110 calculates a
difference between the calculated temperature and the desired
temperature at step 231 and then determines if the difference is
within the threshold at step 235. If not, which is typically the
case for a first iteration, the processor 110 determines if the
calculated temperature is above or below the desired temperature at
step 240. If the calculated temperature is above the desired
temperature, then the emissivity value stored in the memory 120
increases by the step size at step 245. On the other hand, if the
calculated temperature is below the desired temperature, then the
emissivity value stored in the memory 120 decreases by the step
size at step 250. In the event that an additional iteration is
necessary, the step size divides in half at step 255. Step 260
verifies the finite boundaries of the emissivity and, if exceeded,
the process stops at step 270. If not exceeded, another temperature
calculation occurs at step 230 with the new emissivity value. Steps
230 through 260 may repeat as many times as necessary before either
calculating a temperature within the threshold, or exceeding an
emissivity boundary. The reader is encouraged to note that these
steps illustrate a simple binary search, but other convergent
numerical methods are possible.
[0020] Upon calculating a temperature that falls within the
threshold, the emissivity value is saved at step 265 and the
apparatus for measuring temperature 100 is configured to make
repeated measurements of similar objects. This method is
particularly useful in assembly lines where similar parts require
temperature measurement quickly and without physical contact with a
temperature measuring instrument.
[0021] While the aforementioned disclosure presents a method and
apparatus employing a temperature sensing device dependant upon
emissivity, the method and apparatus applies equally to a
temperature sensing device employing multiple infrared wavelengths
to determine temperature in which an appropriate E-Slope must be
determined. The resulting temperature reading is based on the ratio
of the intensities of the two signals that most objects attenuate
equally. This eliminates a dependency on the emissivity of the
object if each wavelength attenuates in the same way. Frequently,
this multi-wavelength approach occurs when the measured object is
in a dusty, moist, and smoke filled area. Therefore, if both
signals propagate through such a medium, they attenuate equally,
resulting in a constant ratio. Unfortunately, not all objects have
the same emissivity at different wavelengths, resulting in
inconsistent attenuation levels when simultaneously measuring both
signals. Such objects are known as "non-greybodies" and create an
unbalanced ratio. A biasing ratio, earlier stated as the E-Slope,
allows correction of this phenomenon and this E-Slope utilizes the
same method as shown in FIG. 2.
[0022] The foregoing description of temperature measurement
devices, methods of measuring temperature and determining
emissivity and E-Slope values have been set forth merely to
illustrate the disclosure and are not intended to be limiting.
Because modifications of the disclosed embodiments incorporating
the spirit and substance of the disclosure may occur to persons
skilled in the art, the disclosure should be construed to include
everything within the scope of the claims to be presented and
equivalents thereof.
* * * * *